The present invention relates to a cammings apparatus for a rotary sprinkler of the type used to irrigate lawns, gardens, vegetable fields and other crops.
Various types of such sprinklers are known and, according to the mechanics of their drives, can be subdivided into three types:
1. Sprinklers operated by the velocity pressure of a jet impacting a member that advances the nozzle of the sprinkler by an angular step;
2. Sprinklers in which velocity pressure of the incoming water is used to drive a kind of a turbine which, via a step-down transmission, drives the sprinkler nozzle in continuous rotary motion;
3. Sprinklers in which the reaction produced by a jet emitted from a tube in a nozzle is converted into a torque which causes the tube to rotate about a vertical axis.
In sprinklers of group 1 the torque produced by the impacting jet is very limited and even minor soiling of either the nozzle or the bearing is liable to stop rotation altogether.
With sprinklers of group 2, the torque acting on the nozzle is quite sufficient--as long as the turbine works, since a gear transmission mission is interposed. The torque acting on the turbine itself is, however, rather small and the slightest fouling is likely to stop the turbine from rotating.
Sprinklers of type 3 tend to rotate at excessive speeds unless effectively braked. Braking, that is, annihiliating part of the kinetic energy of the flowing water is, however, a wasteful and irrational practice.
It is one of the objects of the present invention to overcome the disadvantages of prior-art sprinklers and to provide a sprinkler that operates not on velocity pressure of the water but on the static pressure thereof, therefore producing a torque sufficiently high to ensure proper rotation also under unfavourable field conditions and not using up velocity pressure at the expense of throw, and that, in one of its embodiments, can also be used in what is known as "adjustable angular sweep" mode, in which the sprinkler sweeps out not a full circle, but a sector of a presettable angle smaller than 360.degree..